A shaft supported by magnetic bearings requires a set of auxiliary bearings, also known as “coast down bearings” or “catcher bearings,” to support the shaft when the shaft drops. When the shaft drops onto the auxiliary bearings, the auxiliary bearings support the shaft in a stable position for continued operation or coast down.
Most auxiliary bearing systems utilize co-axially mounted rolling element bearings through which the shaft extends. A clearance exists between an inner race of the rolling element bearings and the shaft. When the magnetic bearings cannot support the shaft, the shaft drops onto the inner race of the rolling element bearing, and the inner race, which is stationary or slow rolling when the shaft drops, spins up and begins to rotate with the shaft until both the shaft and the inner race come to the same speed. This spin up process subjects the rolling element bearings to extreme acceleration and wear which causes damage to the bearing elements, thus limiting the lifespan of the rolling element bearing to a handful of shaft drops.
Other auxiliary bearings generally include a plurality of rollers mounted radially outward from the shaft. The rollers include rolling element bearings disposed therein to support the rollers and allow them to spin freely. When the shaft drops onto the rollers, the rollers engage and rotate with the shaft until both the shaft and the rollers come to the same speed. Conventional auxiliary bearings, however, include complex support structures, and have limited capability to custom tailor damping and stiffness of the bearing supports.
There is a need, therefore, for an improved auxiliary bearing system adapted to support a shaft when an active magnetic bearing fails, or is otherwise shut down, and the shaft drops without the disadvantages noted above.